In view of an increasing shortage of petroleum deposits, the economic exploitation of raw materials containing organic constituents, such as oil, tar sands or oil shale, has become of greater interest. Oil or tar sands are mixtures of clay, sand, water and hydrocarbons. The latter can have different compositions and range from bitumen to normal crude oil. The hydrocarbon content in the sands is between about 1 and 18%. The economic efficiency of exploitation increases with the hydrocarbon content. Oil or tar sands can be recovered by surface mining. When extracting them from deeper soil layers, an initial processing of the oil or tar sand is already effected in situ. Steam is introduced into the deposit in order to liquefy the hydrocarbons. This kind of oil recovery therefore requires a great deal of water, which cannot be discharged entirely free from oil.
Oil shales are rocks which contain bitumen or low-volatility oils. The content of organic matter (kerogen) lies between about 10 and 30%. Oil shales are not shales in a petrographic sense, but layered, not schistous, sedimentary rocks. The recovery of hydrocarbons, such as oil from oil shale, is traditionally effected by mining and subsequent pyrolysis (carbonization at 500° C.). Subsurface recovery (in situ) is alternatively used by pressing a steam-air mixture into the rock previously loosened by blasting and ignition of a flame front, which expels the hydrocarbons such as oil.
The previous recovery of hydrocarbons, such as crude oil from oil or tar sands or oil shale is thus relatively cost-intensive. With rising oil prices, the recovery of hydrocarbons, such as crude oil, from oil or tar sands and oil shale becomes increasingly interesting in economic terms. A problem in the present recovery of hydrocarbons, such as crude oil, from oil or tar sands and oil shales is the necessary high consumption of water and the emission of waste waters containing residual oil.
U.S. Pat. No. 4,507,195 describes a process for coking contaminated oil shale or tar sand oil on solids distilled in retorts. The hydrocarbonaceous solids are mixed with a hot heat transfer material in order to raise the temperature of the solids to a temperature suitable for the pyrolysis of the hydrocarbons. The mixture is maintained in a pyrolysis zone until a sufficient amount of hydrocarbon vapours is released. In the pyrolysis zone, a stripping gas is passed through the mixture in order to lower the dew point of the resulting hydrocarbon vapours and entrain the fine particles. Accordingly, a mixture of contaminated hydrocarbon vapours, stripping gas and entrained fine particles is obtained from the pyrolysis zone. From the contaminated hydrocarbon vapours, a heavy fraction is separated and thermally cracked in a fluidized bed consisting of the fine particles, whereby the impurities together with coke are deposited on the fine particles in the fluidized bed. The product oil vapours are withdrawn from the coking container. As heat transfer material, recirculated solids residues from pyrolyzed oil shale or tar sand is used, which was guided through a combustion zone, in order to burn remaining carbon and provide the heat for the pyrolysis of the raw material. Since there is no pressure seal between the combustion zone and the pyrolysis furnace, the oxidizing atmosphere of the combustion zone can enter the pyrolysis furnace and impair the quality of the oil vapour. Thermal cracking in the coking container also consumes a great deal of energy and is therefore expensive.
EP 1 015 527 B1 describes a process for the thermal treatment of feedstock containing volatile, combustible constituents, wherein the feedstock is mixed with hot granular solids from a collecting bin in a pyrolysis reactor in which relatively high temperatures exist. This should lead to cracking reactions in the gases and vapours in the reactor.
Besides the thermal cracking used in the above-mentioned processes, catalytic cracking processes are also known. In Fluid Catalytic Cracking (FCC), the heavy distillate of a refinery is decomposed to gases, liquefied gases and gasolines, for example, to long-chain n-alkanes and i-alkanes. Cracking is generally effected at temperatures between 450 and 550° C. and a reactor pressure of 1.4 bar by means of an alumosilicate-based zeolite catalyst. FCC crackers are described for instance in U.S. Pat. No. 7,135,151 B1, US 2005/0118076 A1 or US 2006/0231459 A1. An exemplary catalyst is disclosed in WO 2006/131506 A1.
Further possibilities for the further treatment of hydrocarbon fractions include hydrotreatment and hydrocracking.